The present invention relates to key input devices for use in portable telephones and the like, and more particularly to a key input device comprising a plurality of manual keys including a seesaw key adapted to selectively close one of pairs of key contacts.
With reference to FIG. 8, portable telephones usually have a casing 1 formed by a front case 11 and a rear case 12. A display 13 and a plurality of manual keys 14 are arranged on the surface of the front case 11. These manual keys 14 include a seesaw key 15 for use in selecting one of functions. The illustrated seesaw key 15 is adapted to selectively close one of four pairs of key contacts for the selection of the corresponding function.
The casing 1 has a circuit board 3 disposed in its interior as shown in FIG. 9. Arranged on the circuit board 3 are a key sheet assembly 40 to be depressed by the manual keys 14, the display 13, a high-frequency circuit module 32, a vibrator 2 comprising a motor 22 and an eccentric weight 21 attached to the output shaft of the motor for notifying the user of incoming calls, etc.
With reference to FIG. 10, the key sheet assembly 40 has a dome sheet 7 of PET disposed over a base plate 5, with a spacer sheet 60 interposed therebetween, and having a plurality of upwardly bulging dome portions 75. The manual keys including the seesaw key 15 are arranged above the dome sheet 7 for depressing the respective dome portions 75. The spacer sheet 60 is formed with a plurality of circular holes 64 corresponding to the respective dome portions 75 and slotlike air vents 63 interconnecting these circular holes 64 as seen in FIG. 11.
With the key sheet assembly 40, the dome portion 75 is elastically restorably inverted by being depressed by the corresponding manual key to bring a contact terminal 52 provided on the inner surface of the dome portion 75 into contact with a contact electrode 51 provided on the surface of the base plate 5 to close a pair of contacts.
To reliably close the key contacts of the key sheet assembly 40, the contact terminal 52 on the inner surface of the dome portion 75 of the dome sheet 7 must be brought into contact with the contact electrode 51 on the surface of the base plate 5 over as large an area as possible. It is therefore necessary to depress the dome portion 75 vertically downward.
However, in the case of the dome portions 75 to be depressed by the seesaw key 15, a pusher 83 projecting downward from an end portion of the seesaw key 15 depresses the corresponding dome portion 75 in an oblique direction when the seesaw key 15 is moved. Stated more specifically with reference to FIG. 10, the pusher 83 of the seesaw key 15 exerts a depressing force F at an angle of xcex8 with a center axis V extending through the dome portion 75 perpendicular thereto, consequently deforming the dome portion 75 to a distorted form and bringing the contact terminal 52 on the inner surface of the dome portion 75 into point contact with the contact electrode 51 on the base plate 5, hence the problem of failing to close the key contacts reliably.
Accordingly, an object of the present invention is to provide a key input device which is adapted to close key contacts reliably even with a seesaw key.
The present invention provides a key input device which comprises a dome sheet 7 disposed over a base plate 5 and having a plurality of upwardly bulging dome portions 71, and a plurality of manual keys 14 arranged above the dome sheet 7 for depressing the respective dome portions 71, the manual keys 14 including a seesaw key 15 adapted to selectively depress one of dome portions 72 included among the dome portions 71, each of the dome portions 71 being elastically restorably invertible by being depressed by the corresponding manual key 14 to bring a contact terminal 52 formed on an inner surface of the dome portion 71 into contact with a contact electrode 51 formed on a surface of the base plate 5 and close contacts.
The dome sheet 7 has a flat sheet portion 70 formed around the dome portions 71 and comprising an inner region 74 extending inwardly of the dome portions 72 to be selectively depressed by the seesaw key 15, and an outer region 73 extending outwardly of the dome portion 72, a spacer sheet 6 being interposed between the base plate 5 and the dome sheet 7 and being formed with a plurality of circular holes 61 corresponding to the respective dome portions 71, the interposed spacer sheet 6 providing a difference in level from the surface of the base plate 5 between the inner region 74 of the flat sheet portion 70 of the dome sheet 7 and the outer region 73 thereof, the inner region 74 being positioned at a lower level than the outer region 73.
Since the inner region 74 of the flat sheet portion of the dome sheet 7 is at a lower level than the outer region 73 thereof in the key input device of the present invention, each of the dome portions 72 to be selectively depressed by the seesaw key 15 is so inclined as to be positioned at a lower level toward the inner region 74 and at a higher level toward the outer region 73. Thus, each dome portion 72 has its center axis inclined with respect to a perpendicular to the surface of the base plate 5.
When one of these dome portions 72 is pushed by depressing the seesaw key 15, the center axis C extending through the dome portion 72 perpendicular thereto is accordingly positioned in the same or approximately the same direction as the direction in which the depressing force F of the seesaw key 1 acts. As a result, the dome portion 72 is deformed symmetrically about the center axis, bringing the contact terminal 52 on the inner surface of the dome portion 72 into contact with the corresponding contact electrode 51 on the base plate 5 over a sufficient area. Since the dome portion 72 deforms symmetrically about the center axis, this portion 72 enables the user to feel the same sharp click as when with the other manual keys 14 are depressed.
According to a specific embodiment of the invention, the spacer sheet 6 has an opening 65 formed inwardly of circular holes 62 corresponding to the respective dome portions 72 to be selectively depressed by the seesaw key 15 and including the circular holes 62, and the dome sheet 7 has its flat sheet portion 70 joined at the inner region 74 to the surface of the base plate 5 through the opening 65. With this embodiment, a level difference in match with the thickness of the spacer sheet 6 is provided between the inner region 74 of the flat sheet portion 70 of the dome sheet 7 and the outer region 73 thereof.
With the key input device of the present invention, the seesaw key 15, like the other keys, brings the contact terminal 52 on the inner surface of the dome portion 72 into contact with the corresponding contact electrode 51 on the base plate 5 over a sufficient area as described above, whereby the key contacts can be closed reliably.